This invention relates to wind propelled craft and more particularly to an arrangement of a pair of wings of variable dihedral angle in which either wing can provide propulsion from the wind whilst the other provides lift or both wings can be used to generate lift.
The use of counter balancing airfoil surfaces to resist overturning moments from wind propelled craft is taught in several inventions subsequently referenced. The principal weakness in most approaches lies in the inability of the sails or wings to be separately oriented to the longitudinal axis of the craft at all craft speeds and their inability to provide a means of accelerating the craft from rest. Whilst it is well known that the optimum sail orientation for propulsion is approximately vertical, the sail or wing must be able to yaw relative to the craft""s direction of motion between the broad reach and close hauled positions. As craft speed increases, the apparent wind direction moves towards the front of the craft which necessitates trimming the sails inwards. Similarly, any horizontal sail or wing, which is used to develop counter balancing forces, must be able to head into the apparent wind to reduce the cross wind component acting on the airfoil. Whilst there are no known craft which currently successfully use sails to develop, in part or in full, counter balancing moments, some inventions teach various elements which are relevant to this invention.
Sailboards are fast wind propelled watercraft. They combine simplicity of sailing rig with a requirement for skill and agility from the sailor to balance the pull from the hand held sail. Whilst the sail can be tilted about the mast step to generate forward propulsion, sail area is limited by the need to balance sail power with the weight of the sailor standing on a narrow board. The sail can be held at a wide angle to the craft axis on a broad reach when the craft is heading essentially downwind or the sail can be held at a small angle to the craft axis in the close hauled mode. The craft is steered by tilting the sail back so that the center of wind effort is aft of the center-board causing the craft to round up into the wind or the craft can be made to turn away from the wind by tilting the sail forward. High speed may be achieved in strong winds when the sail is angled back towards the wind direction with the weight of the sailor underneath the sail, which then generates propulsive forces and lift. A person skilled in the art can jump the board off waves when travelling at high speed and achieve flight for short distances under the initial momentum by tilting the sail to a horizontal position. However, the non-symmetric shape of the sail above the sailor and the relatively small sail area limits the flight to short distances.
A symmetrical sail for a sailboard is taught by U.S. Pat. No. 4,682,557. This device embodies a symmetrical sail pivoted at the top of a short mast, which is attached to a sailboard. The sail can be tilted horizontally to become a lifting wing when the moving craft is headed into the wind. Their device has no means of enhancing resistance to overturning moments whilst in sailing mode, but the sail is symmetrical in flight when the board is jumped off waves. Both this device and conventional sail boards have sail areas limited to approximately 4.5 to 7 square meters in order to remain manageable in up to moderate wind speeds due to the constraints of strength and weight of a sailor standing on a sailboard. A wing area of this size cannot sustain manned flight for any considerable distance. Each wing of the present invention has an area of approximately 4.5 to 7 square meters giving a combined area in flying mode capable of lifting the weight of the craft and crew.
A craft which utilizes airfoil sections in a dual sail configuration whilst providing increased resistance to the heeling moment is taught by U.S. Pat. No. 3,800,724. This craft embodied two airfoil-cambered wings that tilted about an axis parallel to the fuselage. When the left wing is tilted upwards to develop propulsive forces on port tack, the right wing is tilted horizontally to develop lift and vice versa. A rigid link between the wings ensured mutual dependency. When the craft changes tack, the vertical wing is tilted horizontal and the other wing is tilted vertical. In each case, the lifting side of the airfoil section is favorably presented to the wind. Reference is made to an optional embodiment in which the wings may also pivot about a vertical axis to align the wings to the relative wind for optimum performance. However, this craft required a power source to drive actuators, pistons, a propeller to get up to speed, ailerons, and the like. Furthermore, the fixed link between the wings ensured that when both wings were at the same angle to the horizontal, they were relatively steeply inclined thus reducing their vertical lift component.
A similar vee winged device was described in U.S. Pat. No. 3,987,982. However, this craft had no means of varying the angle between the wings, which were rigidly fixed to the fuselage. As the fuselage consequently had to tilt from one side to the other during tacking, the hull required a special shape and the pilot presumably required a tilting seat. The craft also had no means of pivoting the wings about a vertical axis to permit the driving sail to vary between the broad reach and close haul position relative to the craft longitudinal axis. It consequently would have had difficulties in moving off from rest and getting up to speed. These latter two referenced craft required a vertical rudder and ailerons to vary the angle of attack of the wings to the wind. The craft of the present invention avoids such requirements by incorporating means of controlling a single pair of wings in the wing support spar. This spar provides for tilting of the horizontal wing and a separate capability to correct the movement of the center of effort of the vertical wing that would otherwise occur, by providing a separate sliding movement of the boom along its axis relative to the spar. The requirement in U.S. Pat. No. 3,987,982 to tilt the body from one tack to the other is avoided in the present invention by the use of a universal joint between the body of the craft and the wing support spar. The body of the present invention consequently can have a flat hull such as in a simple sailboard type planing hull with a vertical center board to provide optimal resistance to lateral drift whilst in sailing mode.
A simple approach to providing simultaneous propulsion whilst providing resistance to overturning moments is taught by U.S. Pat. No. 4,674,427. A single straight wing with floats at each end is supported laterally to one side of a narrow hull. During tacking the wing must be flipped end for end to the other side of the hull. Although this device eliminates the overturning moment on the craft body when sailing, it has no means of varying the yaw angle of the sail relative to the craft axis in order to gather speed from rest. This craft would have had difficulties in tilting the sail to the opposite side of the hull during tacking.
A mast pivoting mechanism was taught by U.S. Pat. No. 4,706,590 to reduce heeling moments of the supporting vessel. However, whilst the mechanism provided a means of altering the angle of the mast relative to the hull, the device offered no means of counter balancing the over turning moments from the sail.
Resistance to over turning moments using an adjustable hydrofoil suspension system is taught by U.S. Pat. No. 5,168,824. The system provides for the adjustment of the foil surface""s angle of attack in response to the movement of a float that senses the level of the water""s surface whilst filtering out high frequency undulations using a system of flexible beams. The adoption of two or more such systems of beams to a watercraft permitted control of the heeling forces. Their preferred embodiment comprised two vertically mounted sails supported on buoyant outriggers displaced laterally on either side of a central hull. This craft has achieved very high speeds and confirms the effectiveness of damped flexible floats in controlling the attitude of outriggers and hydrofoils. However, each sail is required to perform equally on either port or starboard tack limiting the development of high performance non-symmetrical airfoil wing type sails. The present invention provides a capability of utilizing such hydrofoils and floats on the far extremities of the wings without the use of additional flexible beams whilst simultaneously using a horizontal wing to provide additional lift.
The above shortcomings of the prior art are overcome by the sailing craft of the present invention. The sailing craft of the present invention comprises a hull and two sails or wings each pivotally connected to a common boom at their inboard end and supported laterally by stays from a central support spar. The dihedral angle between the plane of the sails or wings can be varied between approximately 90 degrees to approximately 175 degrees. A propulsion mode is characterized when the sails are at right angles to each other, or thereabouts; one sail is essentially vertical whilst the other is horizontal and vice versa thereby obtaining propulsion from the upright sail and stabilizing lift from the horizontal sail. Both wings being essentially horizontal characterize a flying mode.
The present invention differs from previous inventions by the pivotal attachment of the lower end of the wings and masts to a common boom, which is supported above the body by the central spar. The spar""s universal joint connection to the body allows the wings to yaw to either side of the body axis to permit broad reaching and close haul sailing from the upright wing. The support spar ensures that the boom is held above the sailor in propulsion mode whilst supporting the weight of the body and sailor from the boom in flying mode. The adoption of a common boom ensures that when the upright wing is in the broad reach position, the horizontal wing is angled forward into the apparent wind to develop lift and provide support to the upright wing. When broad reaching, the apparent wind has a substantial cross wind component to the craft""s heading thus necessitating the need for substantial yaw of the horizontal wing well forward to face into the apparent wind as much as possible to optimize lift. As the craft speed increases, the angle between the craft""s heading and the apparent wind reduces. When close hauled, the boom of the vertical wing is at a minimum angle to the body""s axis and the horizontal wing is almost square to the body axis, at which point neither of the two wings are heading directly into the wind. Lateral drift of the craft is controlled by use of a centerboard and tail fin in the same way as conventional sailboards or yachts. These devices extend below the hull into the water and provide the necessary reaction to determine propulsive forces acting on the craft from the resultant forces. Both wings must be simultaneously controlled in a dynamic environment, the vertical wing for lateral swing angle relative to the body axis and vertical pitch, whilst the horizontal wing must be controlled primarily for angle of attack to the apparent wind. Both movements are permitted by allowing the spar to tilt backwards whilst providing a separate sliding movement of the boom in a guide sleeve attached across the center of the support spar. The overturning and stabilizing moments act about the boom axis within the wing, boom, support spar and rigging system, and are not transferred to the body of the craft.
The present invention provides a means of turning the craft in a similar manner to contemporary sailboard craft. The support spar can tilt backwards towards the stem thus tilting the boom down towards the rear of the craft and the upright mast back, moving the center of effort of the propulsion wing aft of the center board and thus turning the craft into the wind. In order to allow for the down wards tilt of the boom without shifting the center of effort of the propulsion sail, if a straight course is required, provision is made to allow sliding of the boom relative to the support spar. The center part of the boom is covered with a bearing surface to permit the boom to slide forward within the support spar and move the center of effort from the propulsion wing forward in order to make the craft turn away from the wind. Forward tilt of the support spar is limited by a horizontal extension to the support spar at its lower end. The extension ensures that the angle of attack of the horizontal sail is always positive in order to avoid dipping the floats attached to the end of each mast into the water. These floats are required to provide additional support to the horizontal sail when the craft is moving off from rest and the aerodynamic lift forces from the horizontal wing are low.
The craft can be made to tack when underway by tilting the support spar backwards, thus causing the craft to round up into the wind. When both wings are heading equally into the wind the horizontal sail will lift up until both wings are developing equal lift. If the boom is swung across the craft axis towards the wind, the turn of the craft will continue beyond the wind direction under its own momentum and the previously horizontal sail will fly up and become the upright propulsion sail and the craft will be on the opposite tack. Optionally, a rudder can be used to provide separate turning ability without impairment of the principles just described.
Flying mode is achieved by altering the dihedral angle of the wings during the execution of tacking as previously described. The present invention overcomes the problem of yaw instability of a pair of wings with a large dihedral angle between them by providing a simple means of altering the angle between the wings. The angle between the masts can be varied from approximately 90 degrees to approximately 175 degrees by altering the angle between the mast and the support spar. The support spar holding the boom above the body has a lower end and an upper end with the sleeve holding the boom centrally located. Stays extend to each mast from the upper and lower ends. The side stays from the mast are passed through pulleys at the top and bottom of the support spar to form a loop of fixed length. The maximum length of the loop is defined when the sails are both almost horizontal and the spar is vertical. When the center point of the loop to each mast is connected and pulled down towards the hull, it is forced to deviate along a specially shaped guide slot built into the spar to take up the slack that would otherwise be formed. The support spar is thus tilted relative to each mast, reducing the angle between the masts. As both sets of stays are connected to the stay deviator, the support spar always bisects the angle between each mast through symmetry. Fore stays extend from a forward extension of the boom back to each mast to provide forward support to the mast whilst rear support is provided by the connection of the foot of the sail to the boom. Either sail can be tilted essentially upright to derive propulsion from the wind whilst the other is essentially horizontal to develop counter balancing moments, or both sails can be tilted essentially horizontal to derive maximum lift from the apparent wind.
The object of the craft is to obtain sufficient speed from wind propulsion to achieve controllable flight from its own momentum when turning into the wind. The present invention provides a means of achieving controllable flight over short distances by a variation to the tacking maneuver. When the craft is heading into the wind under its own momentum and both sails are generating lift, the dihedral angle between the wings is increased to approximately 175 degrees until both wings are essentially horizontal. As the wings tilt down, the lift from each is automatically balanced and the boom is brought into alignment with the longitudinal axis of the body. If the boom is kept angled down towards the stem above the craft axis instead of pushing it across towards the wind as in the tacking maneuver, then the lift is increased due to the increased angle of attack of both wings. Under favorable conditions and sufficient momentum, the craft will achieve take off. To prevent the body of the craft from hanging down from the universal joint connection with the lower end of the support spar, the lower end of the spar is provided with a forwardly directed foot which engages with the body of the craft under the weight of the crew.
The sail wing system of the present invention is intended to provide a means of compatible transition between wind propulsion across the horizontal plane and take off. Once airborne, the support spar, boom and control bar provides the means of controllable flight in a similar manner to hang gliders. The forward horizontal extension to the support spar automatically provides a balancing cantilever support to the weight of the board and sailor that is aft of the connection of the lower end of the spar and the body of the craft. The body of the craft is consequently automatically supported parallel to the boom. A sliding bearing connection between the boom and the support spar is designed to support the wings and provide a means of moving the weight of the board and sailor forward or aft relative to the center of lift from the wings, to control pitch. By pulling the control bar astern, the center of gravity of the board and sailor is moved forward relative to the center of lift of the wings. Conversely, if the boom is moved forward within the support spar, the center of gravity is moved aft relative to the center of lift. The center of gravity can also be moved to either side of the boom by gently pulling the control bar to the left or right, thus permitting banking and turning. Landing is achieved by pushing the control bar forward and flaring the wings. Under such circumstances, the center of mass moves aft increasing the angle of attack of the wings and precipitating a stall as touch down occurs at the stern. The support spar can then hinge back relative to the body axis maintaining the high angle of attack of the wings whilst the hull skids across the water to provide a gentle landing.